Light emitting diodes (LEDs) are a kind of semiconductor lighting elements, and generally applied to indicators, display screens, and etc. Especially, a type of the LEDs is white LED (WLED) which can be used as a fourth-generation light source to replace fluorescent lamps and incandescent lamps. A theoretical life span of a LED is about 100,000 hours. However, an actual life span of a commercially-available white LED product is generally shorter than the theoretical time of 100,000 hours.
A glue (i.e. a resin or an adhesive) for packaging a light emitting diode (LED) is one of major factors affecting the luminance decay of the LED. Referring now to FIG. 1, a graph of a luminance decay profile of a traditional white LED (WLED) product manufactured by a domestic manufacturer A is illustrated, wherein the traditional white LED product is packaged by a traditional silica gel and continuously tested about 2520 hours under the room temperature of 25° C. and a constant current of 25 mA. The horizontal axis represents time and the vertical axis represents the luminous flux maintenance percentage. As shown, the rate of luminance decay at 168th hour is 13%, the rate of luminance decay at 336th hour is 20%, the rate of luminance decay at 504th hour is 25%, the rate of luminance decay at 648th hour is 31%, the rate of luminance decay at 1128th hour is 49%, and the rate of luminance decay at 2520th hour is 80%. For further verifying the luminance decay condition of the traditional white LED product, the traditional white LED product is continuously tested about 1032 hours under the room temperature of 25° C. and a constant current of 40 mA. Referring now to FIG. 2, a graph of a luminance decay profile of the traditional white LED product tested under the foregoing conditions is illustrated. As shown, the rate of luminance decay at 168th, 336th, 504th, and 1032th hours is 34%, 55%, 68%, and even 88%, respectively. As a result, it is necessary to develop an innovative packaging glue to efficiently reduce the luminance decay of the LED product.